1. Field of the Invention
The present invention relates to a vehicular remote locking/unlocking system wherein a vehicle user equipped with a portable device operates trigger means located in a vehicle and a locking/unlocking means carries out locking/unlocking of an opening member of the vehicle.
2. Description of the Related Art
European Patent No. 0523602 B1 discloses, as shown in FIG. 9, two techniques (i.e., Technique 1 and Technique 2). Technique 1 includes external antennas 2 and 3 directed toward spaces outside a vehicle and having signal transmission ranges indicated as I and II, respectively, and an internal antenna 5 directed toward a space within the vehicle and having a signal transmission range indicated as III. Technique 1 locks and unlocks doors only if a transponder 6 is present outside a passenger compartment, by sequentially transmitting interrogation code signals from the internal antenna 5 and the external antennas 2 and 3 when a start switch (a door outer handle, or a door inner handle) is operated, and sequentially evaluating a received response signal from the transponder 6 to detect the position of the transponder 6. Technique 2 prevents unauthorized unlocking of the doors if the transponder 6 is left behind in the passenger compartment, by sequentially transmitting interrogation code signals with antenna identification codes added thereto and making the transponder 6 only transmit a response signal in response to the interrogation code signals transmitted from the external antennas 2 and 3.
However, because the response signal has to be transmitted even when the transponder 6 is present within the passenger compartment, the number of communications in Technique 1 increases, thereby wasting the power of the transponder 6. There is also the problem that, when the signal transmission range of the internal antenna 5 is reduced due to interference, such as, for example, noise, if the transponder 6 is left behind in a place, such as a door pocket, which is typically positioned on the outermost side within the passenger compartment (a range where I and II overlap), since no response signal is transmitted in response to the interrogation code signal from the internal antenna 5, it is determined that the transponder 6 is present outside the passenger compartment, and a malfunction occurs.
In the case of Technique 2, when the transponder 6 is left behind in the range of III that does not overlap with I, that is, in a middle part of the passenger compartment, unauthorized locking/unlocking can be prevented. However, when the transponder 6 is left behind in a place, such as a door pocket, although the interrogation code signal from the internal antenna 5 is not acknowledged, because a response signal is transmitted to the interrogation code signal that is subsequently transmitted from the external antennas 2 and 3, unauthorized locking/unlocking cannot reliably be prevented.
It should be noted that the signal transmission range referred to here means a range in which the transponder 6 is able to receive the interrogation code signal.